Schottky diode is an important power device and used extensively as output rectifiers in switching-mode power supplies and in other high-speed power switching applications, such as motor drives, switching of communication device, industry automation and electronic automation and so on. The power devices are usually required characteristics of carrying large forward current, high reverse-biased blocking voltage, such as above 100 volt, and minimizing the reverse-biased leakage current.
A number of power rectifiers have been used to provide high current and reverse blocking characteristics. Hsu et al disclosed a Schottky rectifier structure in IEEE ELECTRON DEVICE LETTERS, vol. 22, No. 11, p. 531 (2001); “A Novel Trench Termination Design For 100 V TMBS diode Application.” As is shown in FIG. 1A, the structure includes a plurality of trench type MOS gates 30 and a termination trench 25 formed into n− epi layer 20, which is formed on an n+ substrate 10. The termination trench 25 has spacer like MOS gates 35 formed on the sidewall of the termination trench 25. A patterned insulating layer such as TEOS 40 is then formed on the termination trench 25. The spacer like MOS gates 35 are almost covered by the TEOS layer 40 except a contact 36, which is adjacent to the active region. A patterned metal layer 50 acts as the anode electrode is then formed on the active region to contact the trench type MOS gates 30 and mesas 31 and the contact 36 of the spacer like MOS gate 35.
The Schottky rectifier structure of Hsu disclosed is designed for high voltage and is capable of achieving a reverse blocking voltage over 100 V at an extreme low-leakage current. However, the processes require at least three photo masks: one is for trenches defined, the second is for TEOS defined and the third is for metal extension in the termination region. Thus, an object of the present method is to simplify the processes. According to the present invention, only two photo masks are used.
Another conventional method is disclosed by Chang in U.S. Pat. No. 6,252,288. The structure shown in FIG. 1B includes a plurality of trenches 60 recessed into n− epi layer 52 that is formed on the n+substrate 54. Each of the trenches 60 is formed with an oxide liner 64 on the sidewall and a p+ doping region 66 at the bottom of the trenches 60. The trenches 60 are then refilled with a polysilicon layer 62. A Schottky barrier metal layer 56 served as an anode is then formed and patterned on the resulted surface of the substrate. Finally, another metal layer 158 served as cathode is formed on the backside surface of the substrate opposite to the anode. The area from the midpoint of one trench structure to the midpoint of an adjacent trench structure is referred to as a “cell”.
Chang does not disclose fabricating method of about the forgoing devices. Apart from that, no termination structure is include, and the capability of about prohibiting premature breakdown is doubtful when the device is under reversed biased high voltage since the structure contains only thin oxide liner 64.
An object of the present invention is to propose a high switching speed two mask Schottky diode with high field breakdown and a method of making the same.